Browsing by Author "Cuadros, Angela P."
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Item Coded aperture design by uniform sensing in compressive X-ray tomosynthesis systems(University of Delaware, 2016) Cuadros, Angela P.X-ray tomosynthesis systems are essential in medical diagnosis. They are currently used in mammography, lung nodule detection among other medical applications. As with computed tomography systems, radiation dose is of great concern and new approaches have been recently proposed to address this issue. Coded aperture compressive x-ray tomosynthesis, for example, places a coded aperture in front of an x-ray source in order to obtain patterned projections of a three-dimensional object on a two dimensional detector plane. By using different coded apertures in a multiple source system, multiplexed projections can be obtained instead of sequential projections as in conventional tomosynthesis systems, thus using less measurements which leads to the reduction of radiation. Compressed sensing (CS) reconstruction algorithms are then used to recover the three-dimensional data cube. Random structures for the coded apertures have been proposed before, however they operate poorly in exploiting the inherent projection patterns proper of the system. This thesis proposes an algorithm for the design and optimization of the coded apertures in a multiple source compressive x-ray tomosynthesis system. A uniform energy criteria on the voxels and detector elements is used so that the object is uniformly sensed and the elements of the detector plane uniformly sense the information. Both simulation and experimental results for optimized coded apertures are shown and their performance is compared to the use of random coded apertures.Item Experimental demonstration and optimization of X-ray StaticCodeCT(Applied Optics, 2021-10-18) Cuadros, Angela P.; Liu, Xiaokang; Parsons, Paul E.; Ma, Xu; Arce, Gonzalo R.As the use of X-ray computed tomography (CT) grows in medical diagnosis, so does the concern for the harm a radiation dose can cause and the biological risks it represents. StaticCodeCT is a new low-dose imaging architecture that uses a single-static coded aperture (CA) in a CT gantry. It exploits the highly correlated data in the projection domain to estimate the unobserved measurements on the detector. We previously analyzed the StaticCodeCT system by emulating the effect of the coded mask on experimental CT data. In contrast, this manuscript presents test-bed reconstructions using an experimental cone-beam X-ray CT system with a CA holder. We analyzed the reconstruction quality using three different techniques to manufacture the CAs: metal additive manufacturing, cold casting, and ceramic additive manufacturing. Furthermore, we propose an optimization method to design the CA pattern based on the algorithm developed for the measurement estimation. The obtained results point to the possibility of the real deployment of StaticCodeCT systems in practice.Item Static coded aperture in robotic X-ray tomography systems(Optics Express, 2022-02-22) Mao, Tianyi; Ma, Xu; Cuadros, Angela P.; Dai, XiuBin; Wang, Zhiteng; Zhang, Xin; Zhu, Shujin; Zhu, Jianjian; Arce, Gonzalo R.Coded aperture X-ray computed tomography is a computational imaging technique capable of reconstructing inner structures of an object from a reduced set of X-ray projection measurements. Coded apertures are placed in front of the X-ray sources from different views and thus significantly reduce the radiation dose. This paper introduces coded aperture X-ray computed tomography for robotic X-ray systems which offer positioning flexibility. While single coded-aperture 3D tomography was recently introduced for standard trajectory CT scanning, it is shown that significant gains in imaging performance can be attained by simple modifications in the CT scanning trajectories enabled by emerging dual robotic CT systems. In particular, the subject is fixed on a plane and the CT system uniformly rotates around the r −axis which is misaligned with the coordinate axes. A single stationary coded aperture is placed on front of the robotic X-ray source above the plane and the corresponding X-ray projections are measured by a two-dimensional detector on the second arm of the robotic system. The compressive measurements with misalignment enable the reconstruction of high-resolution three-dimensional volumetric images from the low-resolution coded projections on the detector at a sub-sampling rate. An efficient algorithm is proposed to generate the rotation matrix with two basic sub-matrices and thus the forward model is formulated. The stationary coded aperture is designed based on the Pearson product-moment correlation coefficient analysis and the direct binary search algorithm is used to obtain the optimized coded aperture. Simulations using simulated datasets show significant gains in reconstruction performance compared to conventional coded aperture CT systems.Item Static coded illumination strategies for low-dose x-ray material decomposition(Applied Optics, 2022-01-20) Cuadros, Angela P.; Restrepo, Carlos M.; Noël, Peter; Arce, Gonzalo R.Static coded aperture x-ray tomography was introduced recently where a static illumination pattern is used to interrogate an object with a low radiation dose, from which an accurate 3D reconstruction of the object can be attained computationally. Rather than continuously switching the pattern of illumination with each view angle, as traditionally done, static code computed tomography (CT) places a single pattern for all views. The advantages are many, including the feasibility of practical implementation. This paper generalizes this powerful framework to develop single-scan dual-energy coded aperture spectral tomography that enables material characterization at a significantly reduced exposure level. Two sensing strategies are explored: rapid kV switching with a single-static block/unblock coded aperture, and coded apertures with non-uniform thickness. Both systems rely on coded illumination with a plurality of x-ray spectra created by kV switching or 3D coded apertures. The structured x-ray illumination is projected through the objects of interest and measured with standard x-ray energy integrating detectors. Then, based on the tensor representation of projection data, we develop an algorithm to estimate a full set of synthesized measurements that can be used with standard reconstruction algorithms to accurately recover the object in each energy channel. Simulation and experimental results demonstrate the effectiveness of the proposed cost-effective solution to attain material characterization in low-dose dual-energy CT.